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Edge Superlattice Bloch Oscillator

IP.com Disclosure Number: IPCOM000043791D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Chang, LL: AUTHOR [+3]

Abstract

The possibility of negative-resistance and Bloch oscillation, while predicted theoretically, has eluded experimental verification because of the stringent requirement of a long electron mean free path or a long electron scattering time. An edge superlattice makes it possible to take advantage of the high mobility therein so as to achieve the high-frequency Bloch oscillation. Two configurations are shown in Figs. 1 and 2 where A is GaAs, B is Ga1xAlxAs, and C is Ga1-yAlyAs. The superlattice, with a typical period "d", which is the sum of the layer thickness of A and B, of 100 ˜ can be readily fabricated by molecular beam epitaxy. This structure is then either cleaved or angle-polished and etched and, on its edge, additional depositions are made. In Fig.

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Edge Superlattice Bloch Oscillator

The possibility of negative-resistance and Bloch oscillation, while predicted theoretically, has eluded experimental verification because of the stringent requirement of a long electron mean free path or a long electron scattering time. An edge superlattice makes it possible to take advantage of the high mobility therein so as to achieve the high-frequency Bloch oscillation. Two configurations are shown in Figs. 1 and 2 where A is GaAs, B is Ga1xAlxAs, and C is Ga1- yAlyAs. The superlattice, with a typical period "d", which is the sum of the layer thickness of A and B, of 100 ~ can be readily fabricated by molecular beam epitaxy. This structure is then either cleaved or angle-polished and etched and, on its edge, additional depositions are made. In Fig. 1, the simple version, only one single layer of C is required, which has a typical thickness of N 1000 ~ and a high Al-composition, y > x. The superlattice is undoped, while layer C is doped to, say, an impurity concentration of 1016cm-3 . Electrons are transferred from C to A and B to create the shaded conduction channel. These electrons, dissociated from their impurities, have high mobilities and long scattering time. In Fig. 2, a layer A is deposited on the edge prior to layer C, where A is also undoped with a typical thickness of N100 ~. From a similar transfer process, the conduction channel is now in A, where the electrons still feel the presence of the periodic potential underneath. This structure has the advantages of having the channel completely in GaAs and not on the polished surface of GaAs and Ga1- xAlxAs, where some damage is unavoidable; thus it is easier to achieve the required high mobility. The conditions of operation are as follows. The recently reported mobility in modulation-doped GaAs is N 106cm2/V-sec at low temperatures compared with bulk GaAs mobility of a few thousands, the scattering time,...